1. Field of the Invention
The present invention relates to an image calibration device and the related method, especially to an image calibration device and the related method capable of solving the problem of green color non-uniformity of an image.
2. Description of Related Art
An electronic product such as a digital camera, a video camera, a multimedia cell phone, a monitoring system, a tablet PC, or etc. makes use of a single sensor to take a picture. Such kind of sensor usually takes down the information of red, green and blue colors simultaneously by a Bayer Color Filter Array (Bayer CFA) to reduce the manufacturing cost. As it is shown in FIG. 1, a Bayer CFA 100 includes a plurality of Bayer patterns 110 which is composed of four sensing units. These four sensing units keep the information of red, green, green, blue (R, Gr, Gb, B) colors respectively through a color filter, so as to constitute a basic unit composed of three primary colors. A full color image is then obtained by an interpolation procedure (i.e. a de-mosaicking procedure) processing the raw Bayer CFA image from the single sensor.
The procedure for the generation of the said full color image is shown in FIG. 2. Through a lens 220 and a sensor 230 (including a color filtering array), a raw Bayer CFA image 240 can be obtained from shooting an external scene 210; the raw Bayer CFA image 240 is then processed by an image sensor pipeline (ISP) procedure 250 (including the aforementioned interpolation procedure) and turned into a full color image 260. However, the raw Bayer CFA image 240 often carries the phenomena of image error or fidelity loss due to the manufacturing detects of the lens, sensor, or image sensing module. If the ISP procedure 250 ignores these influences, a lot of unusual patterns visible to the naked eyes will appear on the finally outputted full color image 260. For instance, the problematic sensing unit of a sensor will lead to the bright spot in a picture of deep color or the dark spot in a picture of light color; and the green color non-uniformity (which means the disparity between the green pixels (Gr) arranged with red pixels in the same row and the green pixels (Gb) arranged with blue pixels in the same row in a smooth image area generated under uniform illumination) will lead to the phenomena of fidelity loss such as the maze pattern and color tint of a full color image after the execution of the mentioned interpolation procedure. Therefore, the ISP procedure plays an important role in the quality of the final output image.
In general, an ISP procedure will carry out detection and calibration against problematic pixels and green color non-uniformity of the raw image before executing an interpolation procedure in which the solution to the problematic pixels has been studied a lot while the calibration on the green color non-uniformity is rarely discussed. However, as it is described in the preceding paragraph, the green color non-uniformity will lead to the phenomena of fidelity loss such as the maze pattern and color tint visible to the naked eyes, and thus this problem shouldn't be neglected. Accordingly, some people in this art field bring up calibration techniques to tackle the green color non-uniformity; unfortunately, in these techniques, some requires an independent calibration unit to take care of the green color non-uniformity, which leads to the increase of cost due to the installation of extra buffer memories necessary for the communication between the independent calibration unit and other units while the manner adopted by the independent calibration unit to tell the green color non-uniformity from the texture is still ineffective; some combines a green color non-uniformity calibration unit with an interpolation processing unit to save the employment of extra buffer memories, but the difficulty in telling the green color non-uniformity from the texture remains unsolved, which makes the detail of the calibrated image blurred and causes the loss of the high-frequency information in connection with the image resolution while the mentioned maze pattern is still living.
People who are interested in the prior arts may refer to the following documents: U.S. Pat. No. 5,596,367; and US patent application of publication number 20020167602.